Despite the overall success of total knee arthroplasty in relieving pain, patient-reported dissatisfaction rates are high. Improvement in implant design and crosslinked polyethylene have reduced revision rates due to implant loosening and polyethylene wear. However, ligament instability is now emerging as the primary cause of revision in the short term. Knee instability is multifactorial in origin, and caused by ligament laxity, component alignment, and poor muscle control. While there are several reliable systems for accurate component alignment, ligament balancing remains an art and is largely dependent on the surgeon?s intuition and subjective ?feel?. XpandOrtho has developed an electronic knee ligament balancing system that measures dynamic balance during knee arthroplasty and addresses many of the major deficiencies in the current standards for optimizing soft-tissue balance. This Phase I SBIR has two aims. In Aim 1 we will establish the accuracy of the device in measuring ligament balance while performing knee arthroplasty in cadaver knees; and after changing bone cuts and conducting ligament releases. In Aim 2 we will conduct a pilot clinical study for proof of concept assessment of feasibility, surgeon acceptance and learning curve, and short-term clinical outcomes. This innovative device is a self-contained disposable electronic balancing system with adaptive distraction. Unlike traditional mechanical instruments, our device measures balance over the entire range of flexion. The clinical relevance is in the ability to relate intraoperative balance with postoperative outcome; to gain insights into ?optimal? balance for knees; the potential to develop new recommendations for balancing; and finally closing the gaps between implant design, surgical alignment, and soft-tissue balance for optimizing function. XpandOrtho, Inc was founded in 2013 by Drs. Colwell and D?Lima who have over 4 decades of experience in knee arthroplasty, multicenter clinical trials, and biomechanics research. The team successfully executed challenging projects such as implantation of electronic knee components. XpandOrtho has access to surgeons and patients at Scripps Clinic, and to their state-of-the-art biomechanics laboratory. XpandOrtho received 510(k) FDA approval for their first device. The broad interest in this device from surgeons and industry in reflected in attached representative letters of interest. In a subsequent Phase II we plan to quantify potential links between intraoperative balance with postoperative outcomes and function.